In liquid-cooled, in particular water-cooled, internal combustion engines, the cooling water is pumped by a coolant pump in a closed circuit through cooling ducts of the engine block that supports the crankshaft and of the cylinder head, and the heated coolant is subsequently conducted into an air-water heat exchanger or cooler, where the water is cooled back down by vehicle airflow, or by a ventilator when the vehicle is stationary. The coolant pump that supports a circulation of the coolant is conventionally directly driven by a traction drive, in particular a belt drive, a traction mechanism connecting the belt pulleys of the crankshaft and of the coolant pump. An immediate coupling between the coolant pump and the crankshaft provides that the rotational speed of the pump is a function of the rotational speed of the internal combustion engine. It results from this that, when there is a cold start of the internal combustion engine, the coolant circulates, causing a delay in a desirable fast warming up of the internal combustion engine and in the reaching of an optimal operating temperature connected therewith.
In order to avoid this effect, regulatable coolant pumps are used whose displaced volume flow can be matched to a cooling requirement of the internal combustion engine. Using regulated coolant pumps, frictional losses can be minimized, because as the oil temperature increases the viscosity of the lubricant oil, and consequently the friction, is reduced, which has a favorable effect on the fuel consumption. At the same time, an improved exhaust gas emission is achieved, because the efficiency of the catalytic converter requires a minimum exhaust gas temperature, and a shorter span of time required to reach this temperature has an immediate positive effect on exhaust gas emissions. In the cold running phase of the internal combustion engine, automobile manufacturers desire a coolant flow of ≦0.5 l/h, also referred to as “zero leakage flow.” In the context of a new development of internal combustion engines for achieving energetically and thermo-mechanically improved operation, a savings in fuel of ≧2.5% was realizable under test conditions in connection with optimal thermal management.
As a measure for influencing the displacement volume of a coolant pump, from DE 199 01 123 A1 it is known to allocate to the open impeller a slider that overlaps the blades of the impeller and that modifies the effective blade width and that can be moved continuously in the axial direction and set at any position. The adjustment of the slider between an open position and closed position takes place by rotating a threaded-type guide. The regulatable coolant pump known from DE 100 57 098 A1 has a magnetic coil that works together with an armature disk and is displaceably situated in rotationally fixed, spring-loaded fashion on the drive shaft. Due to friction pads by which the impeller is connected to the armature disk, when the magnet is not energized the impeller is driven.
DE 10 2005 004 315 A1 and DE 10 2005 062 200 A1 show further regulatable coolant pumps in each of which a valve slide is attached that is displaceable in the direction of the axis of the pump shaft in order to influence the flow rate in the pump housing. The annular valve slide forms an outer cylinder that variably overlaps the outflow region of the impeller. According to DE 10 2005 004 315 A1, the valve slide, which can also be designated a guide disk, is electromagnetically displaced by a magnetic coil situated in the pump housing. Alternatively, according to DE 10 2005 062 200 A1 a pneumatically or hydraulically actuated actuator is provided for the displacement of the valve slide.